So, here is the three different types of Pressure measured in Engineering
It is established that the Air possesses some Weight. And due to its Weight, Air must exert some force on the Surface of the Earth. The Density of Air is different at different heights due to its property of Compressibility.
The Density of Air has also varied from time to time due to change in its Temperature and Humidity. Due to these factors, the Atmospheric Pr. of Air can not be calculated. But you can calculate in the case of Liquid.
The Atmospheric Pre. at Sea Level is 1.03 kilogram/centimeter square. It can also be expressed as 10.3 meters of water, in terms of equivalent Water Column or 76 centimeters of Mercury in terms of equivalent Mercury Column.
It is the Pressure measured by Pr. Measuring Instruments. The Atmospheric Pr. on the Gauge Scale is marked as Zero. Actually Gauge Pr. is always above the Atmospheric.
It is defined as the sum of Atmospheric and Gauge Pr. In the case of Vacuums, the Gauge Pr. is a minus, and then the Absolute Pr. will be Atmospheric minus Gauge.
If the Intensity at a point is more than the Local Atmospheric, the difference in these two is called “Positive Gauge Pr.”. However, if the intensity at a point is less than the Local Atmospheric Pressure, the difference in these two is called “Negative Gauge Pr. or Vacuum “.
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